1. Field of the Invention
The present invention relates to a process for forming an organic semiconducting layer with molecular alignment, and more particularly to a process for forming an organic semiconducting layer with molecular alignment by means of forming microgrooves in a photoresist using photolithography.
2. Description of the Prior Art
In recent years, organic semiconducting material has drawn many researchers' attention and has proven to be one of the most popular candidates for fabrication of thin film transistors (TFTs) and various electronic and optoelectronic devices. Sirringhaus et al. of the University of Cambridge use self-organization to produce organic thin film transistor (OTFT) having different anisotropic alignment. It is found that the charge transport efficiency is increased with a better ordered molecular chain. For example, the carrier mobility can be increased by 100 times with a better ordered molecular chain. This proves that the molecular alignment of an organic molecule is a very important factor in enhancing the electrical properties of TFTs. (Nature, Vol. 401, p.685, 1999).
The technology of controlling alignment of an organic molecule can be classified into the following three types.
(1) Self-organization: Sirringhaus et al. produce an organic integrated device including an organic thin film transistor (OTFT) and an organic light emitting diode (OLED). Functional groups in an organic molecule interact with the atom (such as silicon) in a substrate. The interaction provides the organic molecule with better alignment by self-organization. The molecular alignment of the organic molecules in the transistor is thus controlled (Nature, Vol. 401, p.685, 1999).
(2) Rubbing or pulling: In U.S. Pat. No. 6,326,640, first, an orientation layer is formed by mechanical rubbing or electric or magnetic field pulling. Next, an organic layer is formed on the orientation layer. In this way, the organic molecule aligns according to the alignment of the orientation layer.
(3) Solvent annealing: In U.S. Pat. No. 6,312,971, an organic semiconducting film is first deposited on a substrate by printing or spin-coating. A specific solvent is selected, such that the alignment of the organic semiconducting molecule is altered using the vapor of the solvent. The electrical properties of OTFT are thus improved.
The above-mentioned conventional technology can only provide the organic semiconducting molecule with the same alignment over the entire substrate. Different alignments in different regions over the same substrate cannot be achieved.